The bodies of automobiles and other vehicles, including trucks, motorcycles, recreational vehicles, farm equipment, etc. have traditionally been made from sheet metal. Metal parts can be manufactured to have smooth, glossy surfaces that are desirable for automobiles and other vehicles. The good temperature resistance of metal body parts allows them to be conveniently coated using an online coating process. In an online coating process, metal body parts are attached to the chassis of the vehicle and given a first coating that serves in part to provide corrosion-resistance treatment through electrodeposition of a primer, the so-called “E-coat.” The exterior of the vehicle is then treated with additional coating layers that can include a primer surfacer coat, a base coat containing the desired colorants, and a clear coat. During these coating steps, the vehicle body can in some cases be exposed to oven temperatures in excess of 200° C. for as long as at least 30 minutes. In particular, the E-coat can require extended exposure to high temperatures while curing.
It would be desirable to make vehicle exterior parts from polymeric materials because of their light weight relative to metal and the ease with which they can be molded into parts with intricate and complicated shapes. However, the polymeric materials must be able to be molded into articles that, when coated, have very similar or identical color tone, gloss, and short- and long-wave values to coated metal parts on the vehicle. The molded polymeric articles must also have good impact resistance, rigidity, chemical resistance, and dimensional stability.
In an offline coating process, the polymeric parts are coated separately from the rest of the vehicle body and attached after the rest of the body is coated in an online process. This means that the polymeric parts do not need to be exposed to the high temperatures of the online coating process. Disadvantages of this process include that it increases expense and that exact color matching between polymeric and metal parts can be difficult to achieve.
In an inline coating process only metal exterior parts are subjected to the electrodeposition primer coating process and its possible high temperature drying step. Polymeric parts are then added to the body of the vehicle for subsequent coating steps. This, however, requires additional steps in and interruption of the coating process that can introduce dust and other impurities into the process.
Thus, it would be desirable to make polymeric exterior parts that could be attached to the vehicle body prior to the E-coat step and be coated together with any metal parts present using standard online coating processes. This requires the use of polymer compositions that can withstand the conditions used for the E-coat step and subsequent coating steps without heat distortion and deformation.
Such polymeric exterior parts would need to be made from polymer compositions possessing good rigidity at the temperatures used in online coating processes and good dimensional stability when exposed to moisture as well as low coefficients of linear expansion. U.S. patent application publication 2003/0073773 discloses impact-modified polyamide compositions suitable for online lacquering. PCT patent application publication WO 2004/009706 discloses compositions comprising polyamide, impact-resistance modifiers, and a phenol-formaldehyde resin or an oligomeric or polymeric compound that has at least two phenolic hydroxyl groups